Delivery device for the fuel of an internal combustion engine

ABSTRACT

A delivery device for the fuel of an internal combustion engine, having a fuel tank ( 4 ), from which at least one fuel pump ( 14, 18 ) delivers fuel via a fuel supply line ( 10 ) and at least one fuel filter ( 12, 16 ) to a fuel consumer ( 2 ), which is connected to the fuel tank ( 4 ) via a fuel return line ( 20 ), is characterized in that a control device ( 24 ) is connected between the supply line ( 10 ) and the return line ( 20 ), which control device establishes a fuel-conveying connection ( 80 ) between the return line ( 20 ) and the supply line ( 10 ) when the temperature in the fuel tank ( 4 ) falls below a predeterminable threshold temperature and at a predeterminable threshold pressure in the return line ( 20 ).

The invention relates to a delivery device for the fuel of an internal combustion engine, having a fuel tank, from which at least one fuel pump delivers fuel via a fuel supply line and at least one fuel filter to a fuel consumer, which is connected to the fuel tank via a fuel return line. Furthermore, the invention relates to a control device, which is provided in particular for the operation of such a delivery device.

Pressure-controlled or stroke-controlled fuel injection devices can be used for the fuel supply of combustion chambers, in particular of self-igniting internal combustion engines such as diesel engines. The fuel injection devices used are unit-injector devices or unit-pump devices such as common rail systems. Such common-rail injection systems can be used to adapt the injection pressure to the relevant load and the speed of the assigned internal combustion engine. To achieve high specific outputs of such internal combustion engines and to minimize emissions, the aim is to achieve the highest possible injection pressure. The fuel for such fuel injection devices is delivered by fuel delivery devices from a fuel tank by means of a fuel pump via a fuel line to a high-pressure fuel source, usually a high-pressure fuel pump in a manner known per se. The high-pressure fuel source may also be a pressure booster. In common-rail injection systems, the high-pressure fuel source in turn acts on a high-pressure fuel line or high-pressure distributor rail, to which a number of fuel injectors are fluidically connected at least matching the number of combustion chambers to be supplied with fuel. The fuel injectors also each have a fuel return line, which is routed to the fuel tank via a return line.

Document DE 10 2011 009 035 A1 shows a delivery device of the type mentioned above. Because such fuel injection devices having common-rail lines have very small throttle and/or valve opening cross-sections, the fuel must be filtered to ensure a proper long-term functioning of the fuel injectors. It has been shown that, when operating the delivery devices at very low temperatures, there is a risk of disruptions of the proper functioning of the filter devices used, in particular for fuels that are not absolutely free from water.

With regard to this difficulty, the invention addresses the problem of providing a delivery device of the type mentioned at the beginning, which is characterized by a higher operational reliability during operation at low temperatures.

According to the invention, this object is achieved by a delivery device that has the features of claim 1 in its entirety.

According to the characterizing part of claim 1, an essential special feature of the invention is that a control device is connected between the supply line and the return line, which establishes a fuel-conveying connection between the supply line and the return line when the temperature in the fuel tank and/or in the supply line falls below a predeterminable threshold temperature and at a predeterminable threshold pressure in the return line. In this way, during operation at low temperatures, heated fuel from the return line reaches the volume flow in the supply line towards the downstream filter as additional volume. The heating of the volume flow effected by the heat input from the additional quantity permits the fuel filter to operate properly at low temperature conditions.

Advantageously, the control device can be arranged in such a way that it opens into the supply line upstream of a fuel filter, viewed in the direction of fuel flow, and is connected to the return line upstream of a counterbalance valve, which is connected to the fuel tank on the outlet side.

In particularly advantageous exemplary embodiments of the control device, a thermostatic valve is used for presetting the threshold temperature, and a pressure valve is provided for presetting the threshold pressure. Advantageously, the pressure valve is set to an opening pressure, which is lower than the preload pressure formed by the counterbalance valve, such that at low temperature and consequently opened thermostatic valve, fuel from the return line, which does not drain into the tank, is available for the fluid connection via the control device.

The delivery device is designed with particular advantage for an injection system, in which the fuel consumer is formed by the fuel injectors of a diesel combustion engine.

The arrangement can be such that a pre-filter or a main filter is connected upstream and downstream of a delivery pump in the supply line. The pre-filter can advantageously be equipped with a coalescer for water separation.

The subject matter of the invention is also a control device, which is provided in particular for a delivery device according to the invention and has the features specified in claim 6. Accordingly, the control device comprises a housing having a continuous fluid duct between two ports. The fluid duct forms the initial part of the fuel supply line of the associated delivery device, i.e. the line area between the fuel tank and a filter, in particular a pre-filter. A further, third port forms the inlet of a connecting path to the fluid duct, wherein a thermostatic valve and a pressure valve are located in this connecting path.

In advantageous exemplary embodiments, the thermostatic valve has a spring-loaded thermostatic element which, below a predeterminable threshold temperature, supported by the spring force, shortens and opens and otherwise blocks a fluid path between the pressure valve and the fluid duct between the two ports.

In particularly advantageous exemplary embodiments, the pressure valve is a spring-loaded diaphragm valve having a rolling diaphragm, which opens at a predeterminable threshold pressure at the third port and opens a fluid path from this third port to the thermostatic valve located in the connecting path.

With regard to the design of the thermostatic valve, the arrangement can be advantageously made in such a way that a valve disk is arranged between the thermostatic element and an associated compression spring to maintain the spring force, which disk blocks the fluid path between the pressure valve and the fluid duct in the closed position of the thermostatic valve and in its open position releases it.

With regard to the design of the housing, the arrangement can be advantageously made in such a way that the fluid path runs perpendicular to the direction of the fluid duct, that the housing is designed to be multipart, in particular bipartite, and that one housing part holds the thermostatic valve having the fluid duct and the two ports and the other housing part holds the pressure valve having the third port.

If the control device is assigned to a fuel feed device, the two first ports can be connected to the fluid duct and the third port can be connected to the return line of the fuel delivery device.

Advantageously, the control device can be designed as an attachment for a diesel filter device, in particular as an attachment to a pre-filter, which is arranged in the fuel supply line between the tank and the feed pump.

Below the invention is explained in detail with reference to an exemplary embodiment shown in the drawing. In the Figures:

FIG. 1 shows a schematic circuit diagram of an exemplary embodiment of the delivery device according to the invention.

FIG. 2 shows a partly cut-away side view of a fuel pre-filter of the delivery device according to the invention having an attached control device according to the invention, drawn in schematic longitudinal section;

FIG. 3 shows a perspective oblique view of the pre-filter of FIG. 2 having an attached control device;

FIG. 4 shows a longitudinal section of the exemplary embodiment of the control device, wherein an operating condition at a temperature above a threshold value is shown; and

FIG. 5 shows a longitudinal section corresponding to FIG. 4, wherein an operating condition at a temperature below a threshold value and a pressure in a fuel return line above a threshold value are shown.

The exemplary embodiment of the delivery device according to the invention shown in the attached drawing is intended to supply the fuel injection system 2 of a diesel internal combustion engine with diesel fuel to be supplied from a tank 4. In the example shown, the injection system 2 is designed as a common rail system (CR). Such common rail systems permit the adaptation of the injection pressure of fuel into the relevant combustion chambers of the internal combustion engine to the load and speeds of the internal combustion engine in an advantageous manner. The figure shows the fuel injection system 2 or the common rail system in simplified form having a high-pressure distributor rail 6, to which the four fuel injectors 8 are fluidically connected. A fuel pre-filter 12, a low-pressure feed pump 14, a main filter 16 and a high-pressure source 18 are inserted in a supply line 10, which extends up to the distributor rail 6 of the injection system 2 connected to the base of fuel tank 4, viewed in the direction of delivery. A return line 20 is connected to the low-pressure side of the injection system 2, for removing leakage, which return line opens into the tank 4 via a non-return valve 22. The check valve 22 is preloaded in such a way that it opens into the tank 4 at a low preload pressure existing in the return line 20.

A control device 24, inserted between a point 26, located in the return line 20 between the return valve 22 and the injection system 2, and a point 28 located in the supply line 10 between the tank 4 and the pre-filter 12, under certain operating conditions provides a connection path between the return line 20 and the supply line 10. The further figures, in particular FIGS. 4 and 5, show the details of the control device 24, of which FIG. 1 shows solely a symbolic representation. The control device 24 has a bipartite housing having a housing base part or main part 30 and a housing cover 32. The main part 30 has a rectilinear continuous internal fluid duct 34, extending horizontally in the figures, between a first port 36 on the input side and a second port 38 on the output side. When integrated into the delivery device according to the invention, the fluid duct 34 forms a line section of the supply line 10 at the point marked 28. Accordingly, the first port 36 is connected to the tank 4 and the second port 38 to the pre-filter 12.

A third port 40, which is connected to the return line 20 at the point marked 26 in FIG. 1, i.e. between the non-return valve 22 and the injection system 2, is located on the housing cover 32. Bolts 42 are used to bolt the housing cover 32 to the flat upper surface 43 of the housing main part 30, wherein a sealing element 44 is arranged between the main part 30 and the attachment 32 in such a manner that it encompasses a circular cylindrical recess 46, which extends downwards from the flat upper surface 43 of the main part 30. A passage 48 formed in the housing cover 32, which is also circular cylindrical but has a smaller diameter than the recess 46, opens into this recess 46. The upper end of the passage 48, which extends in a vertical direction, opens into a horizontal inlet channel 50, which forms the horizontal extension of the inlet of the third port 40. On the side opposite from the third port 40, a housing insert 52, which is attached using bolts 54, forms the closure of the input channel 50.

The housing insert 52 not only forms the closing part, which closes the inlet channel 50 of the housing insert 52 to the outside on the side facing away from the third port 40, but also contains a pressure valve 56, which controls the passage of fluid between the inlet channel 50 and the passage 48, which is routed from the housing cover 32 to the recess 46 in the housing main part 30. A thermostatic valve 58, which has a movable closing body 60 located inside the recess 46, which closes the mouth of the passage 48 in the closing position shown in FIG. 4 is provided to control the fluid connection between the mouth of the passage 48 and the interior of the recess 46 in the main body 30. A thermostatic element 62 is provided for controlling the closing body 60, which thermostatic element is arranged at the bottom 64 of the recess 46 in such a way that most of its length extends through the bottom 64 into the fluid duct 34 and in operation the fuel flowing in via the first port 36 and originating from tank 4 flows around the thermostatic element and thus responds to its temperature. The thermostatic element 62 is preloaded by a compression spring 66 in such a way that it holds the closing element 60 in the open position shown in FIG. 5 if the temperature is below a threshold temperature. When the temperature is above the threshold temperature and the thermostatic element 62 expands accordingly, the closing element 60 moves into the closed position shown in FIG. 4.

The pressure valve 56 is a diaphragm valve having a rolling diaphragm 68, which is shown in the extended position in FIG. 4 and in the retracted position in FIG. 5. In the extended position (FIG. 4), a closing part 70 of the rolling diaphragm 68 is in tight contact with a sealing edge 72, which is located on a ledge 76 of the inlet channel 50, effectively closing the latter. A spring 74 is used to preload the rolling diaphragm 68 having the closing part 70 into the closed position shown in FIG. 4. According to the effect of the spring 74, the pressure valve 56 is set to an opening pressure existing at the port 40, which is below the opening pressure of the check valve 22, but above the pressure existing at the first port 36 and thus in tank 4.

The thermostatic valve 58 is designed in such a way that the thermostatic element 62, at a predeterminable temperature existing in the fluid duct 34, and thus in the tank 4, presses the closing element 60 against the force of the spring 66 into the closing position shown in FIG. 4, such that, at comparatively lower temperatures, the spring 66 moves the closing element 60 into the open position shown in FIG. 5. The relevant temperature ranges of the thermostatic element can vary depending on the customer or the specific task. In the operating condition shown in FIG. 5, where the pressure valve 56 is opened by the pressure acting in the return flow line 20 via the port 40, a connecting path is formed via the passage 48, the opened thermostat valve 58 and an opening 78 located in the base 64 of the recess 46, via which, as indicated by flow arrows 80, heated leakage fluid from the return flow line 20 reaches the fluid duct 34 as an additional quantity to the volume flow in the fluid duct 34. At the slight overpressure in relation to the tank pressure corresponding to the opening pressure of the pressure valve 56, the additional quantity is fed into a mixing zone designated by the numeral 82 in FIG. 5, in which the heat input of the additional quantity causes the volume flow reaching the pre-filter 12 via port 38 to warm up.

In particular the pressure valve 56 prevents a suction pressure from developing in the return flow line. This is to protect the high-pressure pump. Furthermore, the pressure valve 56 is preferably designed in such a way that one side is open to the atmosphere (ambiance), permitting pressure compensation. A pressure compensation element can be used to protect the rolling diaphragm 68 from dirt carried in from the outside.

As shown in FIGS. 2 and 3, the control unit 24 having the form of a unit consisting of the main housing part 30, the housing cover 32 and the housing insert 52 is mounted directly on the fluid inlet 84 of the pre-filter 12. In the advantageous exemplary embodiment shown, the filter medium 88 of the pre-filter has a coalescence layer, which causes separation if the fuel is not completely anhydrous, wherein separated water drips into a collecting chamber 86 located in the bottom area of the filter housing. 

1. A delivery device for the fuel of an internal combustion engine, having a fuel tank (4), from which at least one fuel pump (14, 18) delivers fuel via a fuel supply line (10) and at least one fuel filter (12, 16) to a fuel consumer (2), which is connected to the fuel tank (4) via a fuel return line (20), characterized in that a control device (24) is connected between the supply line (10) and the return line (20), which control device establishes a fuel-conveying connection (80) between the return line (20) and the supply line (10) when the temperature in the fuel tank (4) and/or in the supply line (10) falls below a predeterminable threshold temperature and at a predeterminable threshold pressure in the return line (20).
 2. The delivery device according to claim 1, characterized in that the control device (24) opens into the supply line (10) upstream of a fuel filter (12), viewed in the direction of fuel flow, and is connected to the return line (20) upstream of a counterbalance valve (22), which is connected to the fuel tank (4) on the outlet side.
 3. The delivery device according to claim 1, characterized in that a thermostatic valve (58) is used for presetting the threshold temperature, and a pressure valve (56) is used for presetting the threshold pressure.
 4. The delivery device according to claim 1, characterized in that the fuel consumer (2) is formed by fuel injectors (8) of a diesel internal combustion engine.
 5. The delivery device according to claim 1, characterized in that a pre-filter (12) or a main filter (16) is connected in the supply line (10) upstream and downstream of a delivery pump (14).
 6. A control device, in particular provided for a delivery device according to claim 1, having a housing (30, 38) with a continuous fluid duct (34) between two ports (36, 38), a third port (40) and a connecting path (50, 48, 78) between this third port (40) and the fluid duct (34), a thermostatic valve (58) and a pressure valve (56) in the connecting path (50, 48, 78).
 7. The control device according to claim 6, characterized in that the thermostatic valve (58) has a spring-loaded thermostatic element (62) which, below a predeterminable threshold temperature, supported by the spring force (66), shortens and opens and otherwise blocks a fluid path (48) between the pressure valve (56) and the fluid duct (34) between the two ports (36, 38).
 8. The control device according to claim 6, characterized in that the pressure valve is a spring-loaded diaphragm valve (56) having a rolling diaphragm (68), which opens at a predeterminable threshold pressure at the third port (40) and opens a fluid path (50) from this third port (40) to the thermostatic valve (58) located in the connecting path (50, 48, 78).
 9. The control device according to claim 6, characterized in that the thermostatic valve (58), the arrangement can be advantageously made in such a way that a valve disk (60) is arranged between the thermostatic element (62) and an associated compression spring (66) to maintain the spring force, which disk blocks the fluid path (48) between the pressure valve (56) and the fluid duct (34) in the closed position of the thermostatic valve (58) and clears it in the open position.
 10. The control device according to claim 6, characterized in that the fluid path (48) runs perpendicular to the direction of the fluid duct (34), that the housing (30, 32) is designed to be multipart, in particular bipartite, and that one housing part (30) holds the thermostatic valve (58) having the fluid duct (34) and the two ports (36, 38) and the other housing part (32) holds the pressure valve (56) having the third port (40).
 11. The control device according to claim 6, characterized in that the first two ports (36, 38) can be connected to the fluid duct (34) and the third port (40) can be connected to the return line (20) of a fuel delivery device.
 12. The control device according to claim 6, characterized in that it is designed as an attachment for a diesel filter device (12). 